Local Exchange to Office 365 (TLS)

Hello,

I have 2 companies:

Company A: Local onsite Microsoft Exchange 2010 (Barracuda SPAM Filter)
Company B: Office 365 Exchange Online (From Microsoft)

From my Barracuda SPAM filter (Company A) I set it to only send and receive mail for Company B using TLS.

I can send and receive fine. I assumed that Exchange on both ends by default uses Opportunistic TLS which I verified for Company A. 

My question is how can I 100% verify that mail transmissions from A to B it is in fact using TLS. I analysed the headers but I am not sure what I am looking for.

I do see this in the header... X-Barracuda-EncryptedAES128-SHA

Thanks